1. components
52 March 2016 | Electronics For You www.efymag.com
T
he need of the hour is higher speed
at lower power consumption. A
laptop is expected to boot-up quickly
and its charge to last for at least a few
hours. Military equipment must function
right in the most stringent conditions. No
one wants to go in search of a particular
kind of charger for a mobile just because
the one he or she has cannot function
on the available alternating current (AC)
power line in another country.
These are scenarios we never give a
second thought to. But essential parts
driving each of these are transistors,
transformers and rectifiers put together on
or around a chip, coming to the fore as a
power supply system. Right from a simple
torch to something as complex as a satel-
lite system, power-conversion components
play a vital role in their functioning. This
article tries to look at the latest develop-
ments in this sector of electronics and
what makes these improvements kick in.
Moving away from silicon
In order to improve system efficiency
and lower the form factor, increasing
the switching frequency of the system is
one viable solution. Critical components
for high-frequency action of power-
management components are metal oxide
semiconductor field-effect transistors
(MOSFETs), accompanied by related driv-
ers. Higher the frequency, higher is the
required gate charge, and it is common
to use MOSFETs in parallel to achieve an
effective lower resistance and higher gate
charge. But, there is also a need to make
sure that switching loss is lower.
Even with all the enhancements in the
silicon wafer, power-conversion compo-
nents ask for more. While going to lower
and lower nodes certainly helps achieve
higher switching frequencies in the order of
GHz, power-related devices demand a MHz
range. Thus, there is a shift towards using
materials like gallium-nitride (GaN) and
silicon-carbide (SiC).
Lower switching loss. GaN and SiC
offer a higher band gap as compared to
silicon, and thus the system design itself
undergoes a change. GaN MOSFETs were,
in the past, mainly used in low-voltage
applications (<100V). Now, GaN based
devices target voltage ranges from 200V to
700V, while SiC based devices target a volt-
age range above 700V. The first 600V-650V
GaN was commercialised by Transphorm
& Efficient Power Conversion Corp. (EPC)
in 2014, and now companies like Infineon
and Texas Instruments (TI) have joined this
trend. Started off by Cree, SiC MOSFETs are
now being manufactured by Microsemi,
STMicroelectronics, Toshiba and Infineon,
to name a few.
Gate-charge driver is as important.
While the main advantage is that GaN and
SiC offer high-frequency support with lower
switching loss, and a smaller form factor,
driving the gate circuit for these materials
requires a negative voltage to be applied,
moving away from the traditional silicon
based approach. To make it easy to cope
with this change, designers are coming up
with specialised drivers.
While there have been efforts to provide
components and drivers in a single pack-
age for easy end use, the design process is
complex. Some vendors prefer to separate
out the two in order to offer more flexibility
in matching existing drivers with transistors
of different ratings.
What Drives Power-Conversion
Components
Priya Ravindran
is a technical
journalist
at EFY
Fig. 1: Comparison of GaN
and Si (Image courtesy:
www.mouser.com)
Draincurrent
(A/min)
Drain-to-source voltage (V)
IV characteristics comparison
between GaN and Si in the same dimension.
(Gate length/width 0.25/1000mm)
On-resistance
Maximum
operating
frequency
Maximum
current
Maximum field
strengh
Si Si
GaN GaN
Tmax
(a.u.)
(a.u.)
(a.u.)
(a.u.)
1
1
1
1
1
(a.u.)

2. 53www.efymag.com Electronics For You | March 2016
powered devices like mobile phones
and wearables perform power con-
version at direct current (DC) range,
and at much lower levels. Battery
is expected to charge fast, be stable
and reliable. A power supply also
needs to tolerate high voltages and
not break down in such scenarios.
To add to the burden, there is the
case of wireless charging.
Many battery-operated systems
use two or more supercapacitors
in series. In an earlier interview,
Spanning a range of voltages
and temperatures
With power-conversion components
present in all kinds of electronic
devices/gadgets, it is imperative for
these to support a range of tem-
perature and voltage operations.
Components are rated according to
grids. Commercial applications are
the ones working at least power
and temperature ranges, but have
to take into account power fluctua-
tions. Ones used under the hood of
automobiles and light emitting di-
odes (LEDs) need to support about
150°C temperature. Reliability and
high tolerance are prime deciders
for military-grade components,
while those that go into space
electronics need to withstand many
kinds of radiations.
Products that work on AC mains
like LED bulbs and inverters take
in 220V AC input and convert it to
high-range voltages. High voltages
demand heavy device capability, and
to support these, there are MOSFETs,
bipolar transistors and insulated-gate
bipolar transistors (IGBTs), compet-
ing in the same space.
Traditionally, voltage handling
was highest for bipolar technology.
With IGBT disrupting this technol-
ogy, it is now common to find IGBT
modules in high-voltage equip-
ment like the uninterrupted power
supply (UPS).
Batteries to the rescue. Battery-
Robert L. Chao, founder, Advanced
Linear Devices Inc., explained how
MOSFET based current balancing
is enabling reduced power use in
superconductor stacks. He says, “A
MOSFET array balances leakage cur-
rents in each cell by exponentially
varying currents relative to selected
operating voltages. This method
compensates for leakage-current
imbalances with small voltage
imbalances so that maximum rated
voltage limits are not exceeded.”
Varying models for different
end applications
While designing power-conversion
components, lifestyle of consum-
ers and application of the system
also define scalability of the design.
Current-handling capability and
failure protection of the designed
circuit reflects its complexity, cost
and size.
Consider the case of a meter-
ing device. Presently, a majority
of digital residential meters are
non-communicative, with no elec-
tronic controlling capabilities. Power
requirement for such systems will
hardly be 0.5W to 2W. However,
futuristic smartmeters look to inte-
grate communication capabilities
and remote control facilities within,
and this would demand a difference
in the design. Thus, system develop-
ers design variant models of power-
sourcing circuits.
Conquering heat
Small sizes and higher packing
densities automatically come with
Harvest energy and use it efficiently
Take the case of a sensor that is fitted into a wall. It is left untouched, but expected to do
its job sincerely, day in and day out. Would someone have to monitor its battery levels
regularly? Instead, put a small board next to it and fit in a solar panel, not unlike modern
electronics calculators. The sun would then take care of keeping the battery charged.
Using brushless DC motors in appliances like fans, variable speed drives for
controlling motors in air-conditioners and refrigerators, and employing smartmeters in
smartgrids helps reduce energy loss and conserve energy.
Further, renewable energy power supplies such as solar/electric vehicles and telecom/
server power supplies demand high efficiencies of nearly 99 per cent. Energy harvesting
also comes into utmost importance when dealing with the Internet of Things applications.
Is AC losing out to DC?
Most appliances used in daily life have a rectifier circuit that converts supplied AC current
into direct current (DC), and store energy or use it to power the system. With solar and
battery-powered technologies gaining importance, DC-to-DC conversion is becoming the
norm. Output of a solar photovoltaic system is low-voltage DC that can be boosted to suit
requirements. These are highly efficient and preferred. It is in the case of home lighting
systems that AC is still preferred, as AC loads with high power rating are easily available.
High-voltage DC transmission (HVDC) is also a growing trend, showing promise in
improving overall system efficiency and renewable energy opportunities. In a white paper,
Stephen Oliver, vice president, VI Chip Product Line, Vicor Corp., has said that, innovative
conversion, control and distribution approaches in power-conversion technology, enabled
by advanced semiconductors and conversion topologies are making HVDC practical for
distribution.
HVDC offers tangible and significant benefits for both sourcing options and system
end-to-end performance. A research by France Telecom and China Mobile estimates that
DC distribution can save eight per cent to ten per cent of power across the board.
Semitrex Technologies,
a Californian start-up,
claims to have come
up with one-size-fits-
all power supply on a
chip, Tronium, which
can provide an output
from 1.8V to 48V. The
design of the chip is
based on a capacitive-
voltage-reduction technology termed
muxcapacitor, and it completely does away
with magnetic and inductive components.
Tronium power
supply SoC (Image
courtesy: www.
semitrex.com)

3. components
54 March 2016 | Electronics For You www.efymag.com
Quad Flat No Leads packaging is
dominant. TO-XX packaging offers a
wide range of small-pin-count pack-
ages for discrete parts like transis-
tors or diodes. Smaller the pack-
age, higher is the professionalism
required to solder the components.
This packaging trend not only
satisfies the need to fit in maximum
things into minimum space but also
takes care of miniscule-size restric-
tions demanded by peripheral com-
ponent interconnect express (PCIe)
cards and wearable devices.
Making performance count
Optimising the performance of a
chip within its limits of cooling,
packaging and power supply capa-
bilities is a mighty challenge. While
dynamic voltage frequency scaling
is one traditional method, MIC95410
7A load switch from
Micrel permits power
partitioning in systems,
and is also capable of
controlling power-up
sequence using a ramp
signal.
A stable and noise-
free source. It is also
necessary to make sure
In the years to come, cars might drive design changes
In a white paper by Arthur Russell, principal applications engineer, Vicor Corp., the author
says that in an electric vehicle scenario, most of the previously mechanically-powered
systems are now implemented as electrical consumers. Power steering is now a high-
power electrically-actuated drive-by-wire system. Air-conditioning uses a brush-less DC or
3-phase AC motor driven compressor and parking brakes use a motor to electrically actuate
the callipers. These systems significantly increase the demand for safe-to-touch 12V power.
that operation of a power-sourcing
circuit is stable and noise-free. In
a sensor based data-acquisition
circuit, a slight change in output of
the powering circuit can result in
large variations in sensor calibra-
tion, resulting in erroneous data.
Thus, precise voltage regulation
of power-sourcing circuits is of
prime importance for maintaining
system integrity.
Improving efficiency. Vicor has
come up with Factorised Power
Architecture (FPA) to solve power-
related performance issues. Enabling
components are integrated power
components called VI Chips. FPA
aims at providing the highest degree
of system flexibility, power density,
conversion efficiency, transient
responsiveness, noise performance
and field reliability.
Design with caution. Design of
the PCB also comes into prominence
when inductive components like
motors and solenoids are involved.
These components tend to create
spikes in current, and PCB parts
have to be designed with optimum
protection to handle this surge.
There is also a need to build isola-
tion into these solutions, separating
the secondary from the effects of the
primary winding of the transformer.
While trends in power-conver-
sion components are not advanc-
ing as rapidly as, say, the Internet
of Things or infotainment, tried-
and-tested new developments are
here to stay. Keep on the lookout
for more.
Fig. 2: Vicor’s FPA: Factorising regulation, isolation and voltage
transformation (Image courtesy: http://powerblog.vicorpower.com)
the drawback of
higher heat generation.
µModule from Linear
Technology facilitates
sharing of the heat-
sink between digital
microcontroller circuits
and the module.
There is also anoth-
er trend that is seen.
Instead of adding heat-
sinks and fans, the
industry is trying to
use the printed circuit board (PCB)
itself to dissipate the heat gener-
ated. There are two developments to
counter this problem. One is to use
a material on the PCB that removes
heat, and/or use multi-layer boards,
and the other is to adopt multi-pur-
pose packaging technologies.
Packaging plays a vital role.
Requirement for reduced package
size has resulted in tiny lead-less
or ball grid array (BGA) packaging
with extremely small pitches. This
requires reduced power consump-
tion, leading to reduced voltages.
Increases in thermal stresses on
chips create a requirement for
thermal pads, for effective heat dis-
sipation. Heat from the chip goes
into the power pad, from where it
is transferred to the surface of the
PCB and then dissipated.
Major contributors to this report
Bhupinder
Kathpalia,
senior application
engineer, Vicor Corp.
Esmond Wong,
VP, business
development and
supplier marketing,
Arrow’s global
components Asia-
Pacific business
Hemant Kamat,
chief technology
officer, Shalaka
Technologies
Vikas Kumar
Thawani,
analog applications
engineer, Texas
Instruments India
Kaustubh
Karnataki,
chief engineer,
FluxGen Engineering
Techologies Pvt Ltd
Sanjay Dixit,
applications
engineer, Texas
Instruments India
Balasubramanian,
Happiest Minds
Technologies